Common piston slapping or something else?
 

In the last few weeks, my 2002 5.4 seems to have that "piston slap" sound more than it ever has at idle. It purrs like a kitten and still runs great, just the noise doesn't seem to go away after start-up. I'm using, as I always have, the Motorcraft FL-820S oil filter. It is due for an oil change in the next 500 miles. Only difference between now and before is the type of oil I am using. I was going away for vacation, and wanted to get the oil changed before I left, as the miles I'd be putting on the Expy would end up way over my maintenance schedule. I've used Pennzoil Platinum 5W-20 for the last 20k miles with no issues. However, the store was out of the PP and all synthetics, so I bought conventional Quaker State 5W-20 for this cycle. I'll be going back to the PP in 500 miles. The change in oil wouldn't cause this slap, would it? As I mentioned above, the engine runs great, so not terribly worried, but the noise all the time at idle does. Thoughts on this? Oil level is at the 'full' mark. Thanks.

It shouldn't have any effect. You sure you don't have a small exhaust leak from a broken manifold stud making noise? I would see what happens after you change the oil again. I always ran Motorcraft 5w20 semi-syn in my 01 with no issues.

Yeah, this definitely isn't an exhaust leak. It has that "tinny" tapping sound to it. Oddly enough, this week, the sound isn't as pronounced as it was last week. Sometimes, I can't even hear it. Changing the oil Thursday night after work. I'll see if it makes a difference and report back. Thanks for the reply, LxMan.

My '03 would sound like someone hittint the left part of the engine with a ball peen hammer for a few days, then quit for a while. I replaced lash adjusters, checked the tensioners and chains from the top, all looked OK. I never did find the problem. It may have been valve guides, as the valves had a lot of slop when I had the cam followers off. It only had 36K on it when I bought it.

my 04 does the same thing its there when i first start it then it goes away for about a min and then it comes right back. I tried everything nothing worked and lost alot of sleep over it. It started doing it around 70,000 and now it has 80,000 on it don't sound any worse don't sound any better. Been told that some of them do it and some don't.

Well, I changed the oil, as I said I was going to do. The store was out of the PP, so I went back to the dependable and trusty Motorcraft 5W-20 Synthetic Blend with a new FL-820S. Noise disappeared. I don't know if it is complete coincidence, but the noise is gone. Even from a cold start in the mornings, the slap goes away after 5 seconds or so. I'll keep monitoring it, though. But, so far so good!